G-AM II Menard Pressuremeter

The G-AM II is a pressuremeter used to measure in situ strength and stress-strain properties of soils and very soft rock.

Description

The G-AM II pressuremeter is an efficient and economical instrument for the evaluation of most ground engineering problems.

The Probe

A cylindrical metal body with an inner rubber membrane and outer protective sheath mounted so as to form three independent cells. The central cell is inflated with water and the guard cells with gas.

The Control Unit

The case houses all the regulators and valves required to reduce and control the pressure applied to the probe cells. It also contains a reservoir which supplies the flow of water to the measuring cell. The volume variations during a test are read on a sight tube.

The control unit comes with gauges in the 0-25, 0–6, and 0–10 MPa, which is the range needed for most soil applications. Two gauges are provided, eliminating the delicate differential pressure gauge.

The Tubing

A coaxial tubing is used to connect the probe to the control

Test Procedure

The probe is placed at testing depth by insertion in a pre-drilled borehole or, in special conditions, driven to the test depth within a slotted casing. Stress control is used to run the test. Equal increments of pressure are applied to the probe and held constant. The volume changes are noted 30 and 60 seconds after each pressure step is reached.

Test Results

An in-situ stress-strain curve is obtained by plotting the injected volume against pressure. The limit pressure PL is the pressure at which failure occurs, and it reflects directly the bearing capacity:

Qa = (C/F) × PL

where: Qa = Allowable bearing capacity
            C = Shape factor
            F = Safety factor

The modulus of deformation E used to calculate settlement is given by:

E = (1 + ν) 2V(ΔP/ΔV)

where: ν = Poisson’s ratio
           V = Initial cavity volume
           ΔP/ΔV = Pressure variation dependent on volume variation

SPECIFICATIONS
CONTROL UNIT
Pressure gauge accuracy ±1% F.S.
Volume scale accuracy ±0.1 cc (by-pass)

±5 cc (normal)

Max. working pressure 10 000 kPa
Pressure supply Compressed nitrogen
PROBE
Diameter 44 mm

(AX)

58 mm

(BX)

70 mm

(NX)

Length 84 cm 70 cm 70 cm
Weight  4.5 kg 4.3 kg 6.4 kg